1. Field of the Invention
The present invention relates to an image forming apparatus and a density correcting method.
2. Description of Related Art
In general, image forming apparatuses, such as a copying machine and a printer, have a density adjusting function.
In the image forming apparatus, output density is likely to vary due to mechanical factors, such as a variation in the state of the apparatus over time, the mounting position of an optical write device, such as a laser unit, the length of an optical passage, the distortion of a lens, the charged state of a drum, and the state of an intermediate transfer unit, or a change in surrounding environment.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2005-246646 relates to a density adjusting function. JP-A No. 2005-246646 discloses an image forming apparatus.
The image forming apparatus stores image data of a color pattern in which predetermined color (Y, M, and C) patches and color (PCBk) patches obtained by shifting color components of the colors (Y, M, and C) by a predetermined value are arranged such that the tone of the color patch is substantially continuously changed together with identification information corresponding to each of the color patches. Then, the color pattern is output on the basis of the image data of the color patches. When the identification information of the color patch is input to the output color pattern, a color correction table corresponding to the input identification information is used to correct the color of image data to be output.
However, the image forming apparatus disclosed in JP-A No. 2005-246646 uses a color pattern having a, plurality of color patches on a sheet to perform density adjustment. For example, the color pattern needs to be formed in order to adjust only the density of Y (yellow). Therefore, colors other than the color to be subjected to density adjustment are also used to form the color pattern. As a result, toner is unnecessarily used.
In addition, the density adjustment performed by the image forming apparatus disclosed in JP-A-2005-246646 is not density unevenness correction for obtaining uniform density in the main scanning direction. Since density unevenness occurs due to a color (output color) used to form an image or the density of the output color, it is necessary to adjust the density of each output color. For example, when four output colors, that is, Y (yellow), M (magenta), C (cyan), and K (black) are used, it is necessary to adjust the density of each of the colors and mixed colors thereof. When density unevenness adjustment is performed and an image with density including the adjusted output colors is formed and output, paper or toner is unnecessarily used.